1. Technical Field
This invention relates to diagnostic devices for analyzing blood and other liquids in analytical instruments and more particularly to shields for such devices intended to confine the excess liquid to the diagnostic device and to prevent contamination of the instrument.
2. Background
U.S. Pat. Nos. 4,868,129 and 4,946,795 and U.S. application Ser. No. 117,791, filed Nov. 5, 1987, now U.S. Pat. No. 5,077,017 issued Dec. 31, 1991, disclose disposable diagnostic devices in the form of a cartridge which, with the use of a monitor, can be used to automatically dilute a sample of blood and determine the analytical values of various components of blood. Such instantaneous determination of such tests is of great value both to patients and to physicians in that it permits prompt diagnosis of a disease state, prescription of appropriate medication, and monitoring of the proper dosage of medication. While the present invention has broad applications beyond these specific examples, they will be used throughout this application as typical applications.
Each of these devices mentioned above is roughly two-thirds the size of a conventional audio cassette tape and is a single use disposable item. They are used with suitable monitors about the size of a medium-sized audio cassette player that have a receiving slot therein into which the cartridge is partially inserted in preparation for the measurement. Each cartridge has a liquid receiving area which remains outside the monitor and into which the liquid to be analyzed is deposited, such as blood added directly from a pricked finger or by using a capillary tube, syringe, or the like.
Two related problems and disadvantages have been recognized, and the present invention has been developed to solve both of them. Both problems are related to the occasional, inadvertent seepage of excess or misapplied liquid from the surface of the cartridge into the interior of the monitor. This seepage can be caused by gravity flow, but it is often assisted by capillarity, as the cartridge closely fits into its receiving slot and forms numerous spaces of capillary dimensions around its perimeter.
In severe cases, seepage can occur so that the diagnostic system within the monitor will not operate properly. Specifically, internal sensors present in the monitors for the cartridges described above, such as light sensing transducers and other instruments, can be affected by the unintentional presence of liquid, such as blood. If, when the self-diagnostic check is being run, the readings from the sensors are outside of the expected ranges, the monitor will withhold the reporting of any test results until the readings return to the normal range, which cannot happen with contaminated instruments until the instrument is cleaned.
A related problem, apart from having liquid interfere with the operation of the monitor, is the contamination of the monitor which results from contact of a biological test liquid, such as blood, with either the interior or exterior of the monitor. Not only is such contact unsightly and unsanitary, but the hazards of cross-contamination of cartridges with potentially infected bodily liquids of the test subject and the desirability of preventing such contact are so apparent as to require no detailed elaboration. Although surface spills cannot always be avoided and must be cleaned up by the user with care being given to possible infectivity, spills that reach the interior of a monitor can cross-contaminate other cartridges without being recognized by the user. Thus, systems that protect the interior of the monitor from contamination are highly desirable.
A number of these problems have been solved in the laboratories of the present inventors for a different type of cartridge described in U.S. Pat. No. 4,756,884. This cartridge is similar in that it also fits into a monitor and has a liquid receiving area which remains outside the monitor and onto which blood is deposited for analysis. However, this earlier device is not intended for dilution and is therefore smaller than and of a different shape from the devices for which the present invention was developed. The former cartridge was relatively flat, with a broad upper surface. The newer cartridges are tall and narrow. Accordingly, the problem of blood contamination of the monitor using the earlier cartridges, which is described in U.S. Pat. application Ser. No. 341,757, filed Apr. 21, 1989, now U.S. Pat. No. 4,952,373, issued Aug. 28, 1990, was solved in a manner that cannot be directly applied to the present situation. This solution involved a blood shield which comprised a resilient member which, in its free state, projects away from the surface of the device to a distance sufficient to assure that it covers any gap between the liquid receiving surface of the device and the monitor in order to confine excess liquid to the surface of the device and prevent it from entering the monitor. The shield was generally provided with sufficient resiliency to permit it to lie flat with the cartridge in its packaged state, but to automatically project upward when the package was opened so that the device is ready for use.
However, this type of shield is not appropriate for all types of devices, particularly devices in which contamination is likely to occur on more than one surface of the inserted cartridge. In such cases, particularly when the cartridge is designed to be inserted into a top or side surface of the monitor, contamination could occur at the corners of such device, where it would not be possible to provide protection with the flexible, pop-up shield as described. Accordingly, there remains a need for further development in shielding the interior of analytical instruments (monitors) from contamination by blood or other liquids misapplied to a cartridge inserted in the monitor.